1. Technical Field
The present invention relates to a traffic control apparatus for an asynchronous transfer mode (ATM), and more particularly, relates to an ATM traffic control apparatus and method for adaptively controlling various kinds of ATM traffics to maintain quality of service (QoS) and avoid cell congestion.
2. Related Art
Asynchronous Transfer Mode (ATM) is a network protocol designed to efficiently provide service for a wide variety of applications such as high speed digital voice, video and data signals. Each of these applications has different service requirements in terms of cell loss and cell delay. For example, voice traffic can withstand a small amount of cell loss, but it is intolerant to cell delay. Video traffic can typically tolerate a small amount of cell loss, however, it is sensitive to cell delay. Data traffic, such as file transfers, can withstand a considerable amount of cell delay, but it is intolerant to cell loss. To accommodate these differences, each traffic is typically placed in a preassigned queue, each with a different service priority. During periods of network traffic congestion (due to excess arriving traffic), when network traffic demand exceeds the network's bandwidth capacity, servicing algorithms are typically employed to discriminate between different types of traffics in order to allocate bandwidth. Delay is managed by properly sizing the queue depths and prioritizing transmission within a specific type of traffic based upon a measure of the time that an ATM cell has been in the network.
Even with sophisticated queuing and service algorithms, traffic congestion can still occur. There have been several congestion control proposals for ATM networks. These congestion control proposals include traffic control mechanisms for controlling ATM traffic to avoid congestion, as disclosed, for example, in U.S. Pat. No. 4,984,264 for Call Admission Control Method And Cell Flow Monitoring Method In The Same Method issued to Katsube, U.S. Pat. No. 5,179,556 for Bandwidth Management And Congestion Control Scheme For Multicast ATM Networks issued to Turner, U.S. Pat. No. 5,197,127 for Expert System Method For Performing Window Protocol-Based Data Flow Analysis Within A Data Communication Network issued to Waclawsky et al., U.S. Pat. No. 5,276,677 for Predictive Congestion Control Of High-Speed Wide Area Networks issued to Ramamurthy et al., U.S. Pat. No. 5,280,483 for Traffic Control System For Asynchronous Transfer Mode Exchange issued to Kamoi et al., U.S. Pat. No. 5,313,454 for Congestion Control For Cell Networks issued to Bustini et al., U.S. Pat. No. 5,530,695 for UPC-Based Traffic Control Framework For ATM Networks issued to Dighe et al., U.S. Pat. No. 5,581,544 for Method And Apparatus For Evaluating QOS In ATM Multiplexing Apparatus In Which Priority Control Is Performed And For Controlling Call Admissions And Optimizing Priority Control On The Basis Of The Evaluation issued to Hamada, U.S. Pat. No. 5,583,792 for Method And Apparatus For Integration Of Traffic Measurement And Qeueing Performance Evaluation In A Network System issued to Li et al., U.S. Pat. No. 5,654,962 for Error Detection And Correction Method For An Asynchronous Transfer Mode (ATM) Network Device issued to Rostoker et al., U.S. Pat. No. 5,675,576 for Concession Control System And Method For Packeting Switched Networks Providing Max-Min Fairness issued to Kalampoukas et al., U.S. Pat. No. 5,689,500 for Multistage Network Having Multicast Routing Congestion Feedback issued to Chiussie et al., and more recently, U.S. Pat. No. 5,696,764 for ATM Exchange For Monitoring Congestion And Allocating And Transmitting Bandwidth-Guaranteed And Non-Bandwidth Guaranteed Connection Calls issued to Soumiya et al. Many of these traffic control proposals are susceptible to time delay, difficulty in satisfying quality of service (QoS) demanded by users, and to abrupt environmental change in the ATM network.
Other proposal of congestion control in ATM networks is a congestion prevention technique as described in "Survey of Traffic Control Schemes and Protocols in ATM Networks" by J. J., BAE and T. Suda, in Proc. IEEE, vol. 79, pp. 170-189, February 1991. Such a congestion prevention technique is designed to prevent congestion before the congestion is inevitable. The intended purpose is to ensure that the network traffic does not reach a level which causes unacceptable congestion. However, the analysis of offered traffic and network state is not suitable for handling a wide variety of ATM traffics, the high quality of service (QoS) demanded by users and the diversity by the combinations. Moreover, such a congestion prevention technique is also not flexible to unexpected changes in traffic characteristics.
As a result, we have observed that an ATM network must be equipped with a highly sophisticated and flexible congestion control function to effectively avoid congestion and to efficiently maintain high quality of service (QoS) for each traffic source in accordance with unexpected changes in traffic conditions. Moreover, the ATM network must include an intelligent control mechanism to handle a wide variety of ATM services and the diversity by their combinations.